The Pope is expected to focus on the need for peace in a conflict-torn world facing the biggest refugee crisis since the Second World War when he addresses the United Nations later this month.

Archbishop Bernardito Auza, the Vatican's apostolic nuncio and UN ambassador, said the pope's address, in his native Spanish, to world leaders at the 193-member General Assembly on September 25 will likely stress poverty and bad government as drivers of conflict and migration.

He said the plight of tens of thousands of migrants seeking safety and a new life in Europe will be touched on in the pope's UN speech because it is an international issue and "a universal problem".

The archbishop said Francis' two and a half-hour visit to the United Nations will be the fifth by a pope and the shortest because of time constraints.

Archbishop Auza also told reporters that the pope will meet Russian president Vladimir Putin, whose country holds the rotating presidency of the UN Security Council this month.

But Russia's UN Ambassador Vitaly Churkin told reporters: "President Putin will not be here on September 25." Putin has met the pope at least twice previously.

The archbishop responded: "I have not been informed so far that the president will not be there. I will consult the UN ... If the president is not there, the meeting will not take place."

He also said the pope is expected to express appreciation in his General Assembly speech for the UN role in trying to minimise conflict and alleviate suffering - but he said the world body has also seen "lots of failures".

"There is no greater failure of the UN than to be incapable, unable to prevent what is going on in the Middle East now and North Africa," the archbishop said.

Immediately after he leaves UN headquarters, Francis will head to the site where the World Trade Centre stood before the September 11 2001 attacks, a visit archbishop Auza said the pope insisted upon.

During his UN visit, Francis will have a one-on-one meeting with UN secretary-general Ban Ki-moon and then a larger meeting with UN and Vatican officials, archbishop Auza said.

He will then address UN staff members and hold private meetings with the outgoing and incoming assembly presidents.

The pope will be staying at his residence on New York's fashionable upper East Side, which was given to the Holy See in the 1970s as the residence for its UN representative by the family of New York mayor Hugh Grant, who built it and died there in 1910.